Successful attempts since the beginning of this century to remove caffeine from coffee on account of its physiological effects have resulted in a relatively large number of processes which aim in various ways to reduce the concentration of this alkaloid not only in coffee but also in tea. These are generally extraction processes in which the material, moistened with water or steam, is treated with organic solvents which selectively remove the caffeine. The isolation of the caffeine and the recovery of the solvent is then effected by distillation.
The problems associated with the solvent contact, i.e., contamination of the extracted material, have recently been overcome by decaffeinating processes using carbon dioxide as a physiologically tolerable extracting agent. In accordance with the teaching of German Patent No. 2,005,293, caffeine is removed from raw coffee with moist, super-critical CO.sub.2, and after liquefying the CO.sub.2 current the caffeine is removed by adsorption onto activated carbon. According to German Pat. No. 2,212,281, in which the caffeine extraction from raw coffee is effected with liquid CO.sub.2, the caffeine adsorption is also carried out preferably with activated carbon. In German Pat. No. 2,119,678, the removal of caffeine is effected from ground roast coffee; first the aroma oil is removed from the coffee with super-critical dry CO.sub.2, and then, after moistening, the caffeine is removed. The separation of the caffeine from the gas current is effected, besides adsorption with activated carbon or kieselguhr, by reducing the pressure or altering the temperature. A similar process for tea is described in German Pat. No. 2,127,642. In this case, too, after previous aroma removal, decaffeination of the moist tea is carried out with super-critical CO.sub.2 and the caffeine is separated by reducing the pressure or changing the temperature of the gas.
In the two first-mentioned processes according to German Pat. Nos. 2,005,293 and 2,212,281, the activated carbon used for the caffeine adsorption must be regenerated. Regeneration of the carbon, which involves on the one hand removal of the caffeine and in particular of the caffeine residues, and on the other hand the reactivation of the adsorption agent, is a very expensive process since the adsorption bond between the carbon and the caffeine is very strong. When using activated carbon in the known processes, i.e., both in the case of a pressure change in the CO.sub.2 system (pumping up to operating pressure, blowing off the CO.sub.2) and in the case of regeneration, there is unavoidable dust formation and particle disintegration in the structure of the activated carbon, as a result of which fines are produced. Re-use of the carbon material extremely limited, which restricts the economy of the process. A further disadvantage of activated carbon is its inadequate selectivity for caffeine, because other constituents of the coffee are also adsorbed, which, especially in view of the sensory properties of the caffeine-free product obtained, can be a disadvantage. Other methods of separating the caffeine from the gas current require changes of pressure and temperature which are unfavorable as regards energy consumption; for example, the pressure of the caffeine-containing gas current must be reduced considerably to achieve separation.